The present invention relates to an image forming system for forming an image by use of PDL (Page Description Language) data received from a host computer, etc.
There has hitherto been an image forming system for printing on a print-job basis. A print job is defined as a data set extending over a plurality of pages in a case where, for instance, a certain user prints document data extending over the plurality of pages by utilizing an application software in the host computer.
In this image forming system, printing is performed in the following way. To be specific, at first, the host computer, etc. generates a PDL (Page Description Language) job (containing, for example, PDL page data for a plurality of pages) and sends this PDL job to a printer controller. The printer controller having received the PDL job converts each set of PDL page data of the PDL job into raster data, and generates a raster job by assembling pieces of raster data. The printer controller sequentially takes out the raster data of the raster job and sends the raster data to a printer. The printer having received the raster data forms an image on a sheet by use of the raster data.
In the image forming system described above, a case of hybrid-printing a plurality of PDL jobs involved using a method of generating one PDL job by editing the plurality of PDL jobs on the host computer.
Further, there was an alternative method of generating a raster job by rasterizing the PDL jobs received from the host computer, storing this raster job in a storage unit on the printer controller, then generating raster data by rasterizing image data received from a scanner, a FAX, etc., and storing the same raster data in the storage unit described above. According to this method, when the printer controller receives a hybrid print demand from the host computer, one raster job is generated by editing the raster job/raster data in the storage unit described above (such as hybridizing the raster job/raster data on, e.g., a page-by-page basis).
There were, however, problems inherent in the conventional hybrid printing methods including the methods given above.
Namely, there arose a problem that a capacity of the storage unit becomes deficient in the case of hybrid-printing, for instance, a large quantity of raster jobs. That is, when storing the large quantity of raster jobs, etc. in the storage unit in order to hybrid-print the raster jobs, the storage area (capacity) comes to a deficiency, and hence it happened that all the raster jobs were unable to be accumulated in the storage unit.
There was another problem, wherein it is difficult in reality that the image data from the scanner or the facsimile (FAX) are utilized for applications other than printing. Namely, the image data from the scanner or the FAX are, as explained above, stored in the state of being converted into the raster data in the printer controller. Generally, the raster data are not, however, generated in a format suited to the host computer, etc. It is therefore difficult to utilize the image data from the scanner or the FAX to the applications other than printing.
Further, there was a problem in which an image quality declines in the case of hybrid-printing the respective raster jobs with their sheet output directions (printing directions) different from each other. Namely, in the case of printing the respective raster jobs of which the sheet printing directions are different from each other (in the case of using, e.g., a staple function), it is required that the printing directions of the raster jobs be unified in a vertical or lateral direction. That is, if the printing direction of a certain raster job is set in the vertical direction while the printing direction of a different raster job is lateral, the printing directions of the two raster jobs are required to be unified. To be more specific, it is required that, for instance, each set of page data (each set of raster data) held by the different raster job be converted into data rotated through 90 degrees. The raster data have, however, already undergone a gradation process (screening) taking the sheet output direction (printing direction) into consideration when rasterized from the PDL page data. Hence, if the data conversion described above is executed, an original gradation state can not be kept. Consequently, when printing the post-converted raster data, the image quality declines. Accordingly, when the great majority of raster data to be hybrid-printed are converted, it follows that a large decline of the image quality occurs on the whole.
Moreover, in the case of hybrid-printing in a way that uses a plurality of raster jobs for color printing, as a result of the hybrid-printing, a color tone balance between the pages might be lost. Namely, there might differ color-related settings (e.g., a sharpness setting, a photo/text mode setting, etc.) for the respective raster jobs, and an environment (for instance, a setting of the application) on the host computer which has generated the PDL jobs corresponding to the respective raster jobs. In such a case, as a result of printing, there occurs a scatter in the color tones of the respective pages.